1. Field of the Invention
The present invention relates to a high-pressure fuel supply assembly used in a cylinder-injected engine, for example.
2. Description of the Related Art
FIG. 6 is a block diagram showing a construction of a conventional high-pressure fuel supply assembly 100, and FIG. 7 is a partially cut away general cross section of the high-pressure fuel supply assembly 100.
This high-pressure fuel supply assembly 100 includes:
a low-pressure regulator for pressurizing low-pressure fuel to a predetermined pressure, the low-pressure regulator being disposed in a low-pressure fuel intake passage 3 through which flows low-pressure fuel conveyed by a low-pressure fuel pump 2 within a fuel tank 1; PA1 a low-pressure damper 5 for absorbing surges in the low-pressure fuel, the low-pressure damper 5 being disposed in the low-pressure fuel intake passage 3; PA1 a high-pressure fuel pump 6 for pressurizing low-pressure fuel from the low-pressure damper 5 and discharging it into a high-pressure fuel discharge passage 7; PA1 a high-pressure damper 8 for absorbing surges in the high-pressure fuel flowing through the high-pressure fuel discharge passage 7; PA1 a high-pressure regulator 10 for adjusting high-pressure fuel to a predetermined pressure, the high-pressure regulator 10 being disposed in a branch passage 9 branching from the high-pressure fuel discharge passage 7 at a branch portion 18; and PA1 an orifice 11 disposed in the high-pressure fuel discharge passage 7 between the high-pressure damper 8 and the branch portion 18. Moreover, 12 are filters, and 17 is a drainage pipe connecting the high-pressure regulator 10 to the fuel tank 1. PA1 a casing 30 housing the valve assembly 20 inside a first recess 30a; PA1 a cylindrical sleeve 31 housed in surface contact with the second plate 23 of the valve assembly 20; PA1 a piston 33 slidably inserted inside the sleeve 31 forming a fuel pressurization chamber 32 in cooperation with the sleeve 31; and PA1 a first spring 36 disposed between a recessed bottom surface 34 of the piston 33 and a holder 35, the spring 36 applying force to the piston 33 in a direction which expands the volume of the fuel pressurization chamber 32. PA1 a housing 37 fitted over the sleeve 31; PA1 a ring-shaped securing member 38 securing the valve assembly 20, the sleeve 31, and the housing 37 inside the first recess 30a of the casing 30 by fitting over the housing 37 and engaging the first recess 30a of the casing 30 by means of a male thread portion formed on an outer circumferential surface of the securing member 38; PA1 a metal bellows 40 disposed between the housing 37 and a receiving portion 39; PA1 a second spring 41 compressed and disposed around the outside of the bellows 40 between the housing 37 and a holder 42; and PA1 a bracket 43 disposed to surround the second spring 41, the bracket 43 being secured to the casing 30 by a bolt (not shown). PA1 a tappet 44 slidably disposed in a slide bore 43a in an end portion of the bracket 43; PA1 a pin 45 rotatably suspended to follow the shape of a cam (not shown) as a cam shaft rotates and to reciprocate the piston 33; and PA1 a bush 46 and a cam roller 47 each rotatably fitted onto the pin 45. PA1 a first case 50; PA1 a second case 51 disposed opposite the first case 50, the second case 51 forming a space in cooperation with the first case 50; and PA1 a thin, flat disk-shaped stainless steel diaphragm 54 dividing the space into a back-pressure chamber 52 charged with high-pressure gas and a buffer chamber 53. The diaphragm 54 moves so that the pressure of the fuel flowing into the buffer chamber 53 from the high-pressure fuel discharge passage 7 is equalized with the pressure of the high-pressure gas in the back-pressure chamber 52, thereby changing the volume inside the buffer chamber and absorbing surges in the fuel in the high-pressure fuel discharge passage 7.
The above high-pressure fuel pump 6 includes: a valve assembly 20 for opening and closing the low-pressure fuel intake passage 3 and the high-pressure fuel discharge passage 7; and a high-pressure fuel supply body 21 for pressurizing low-pressure fuel from the low-pressure fuel intake passage 3 and discharging it into the high-pressure fuel discharge passage 7.
FIG. 8 is a cross section of the valve assembly 20, the valve assembly 20 including: a first plate 22; a second plate 23; and a thin, flat valve main body 19 positioned between the first and second plates 22 and 23. A first fuel inlet 24 connected to the low-pressure fuel intake passage 3 and a first fuel outlet 25 connected to the high-pressure fuel discharge passage 7 are formed in the first plate 22, the inside dimensions of the first fuel outlet 25 being larger than the inside dimensions of the first fuel inlet 24. A second fuel inlet 26 having inside dimensions larger than those of the first fuel inlet 24 and a second fuel outlet 27 having inside dimensions smaller than those of the first fuel outlet 25 are formed in the second plate 23. The valve main body 19 is provided with: an intake-side tongue 28 interposed between the first fuel inlet 24 and the second fuel inlet 26; and a discharge-side tongue 29 interposed between the first fuel outlet 25 and the second fuel outlet 27.
The high-pressure fuel supply body 21 includes:
The high-pressure fuel supply body 21 also includes:
The high-pressure fuel supply body 21 also includes:
The above high-pressure damper 8 is screwed into a second recess 30b in the casing 30. The high-pressure damper 8 includes:
In a high-pressure fuel supply assembly 100 having the above construction, the piston 33 is reciprocated by the rotation of the cam secured to the cam shaft of an engine (not shown) by means of the cam roller 47, the bush 46, the pin 45, and the tappet 44.
When the piston 33 is descending (during the fuel intake stroke), the volume of the inside of the fuel pressurization chamber 32 increases and the pressure inside the fuel pressurization chamber 32 decreases. When the pressure inside the fuel pressurization chamber 32 falls below the pressure at the first fuel inlet 24, the intake-side tongue 28 of the valve main body 19 bends towards the second fuel inlet 26, allowing fuel in the low-pressure fuel supply passage 3 to flow through the first fuel inlet 24 into the fuel pressurization chamber 32.
When the piston 33 is ascending (during the fuel discharge stroke), the pressure inside the fuel pressurization chamber 32 increases, and when the pressure inside the fuel pressurization chamber 32 rises above the pressure at the first fuel outlet 25, the discharge-side tongue 29 of the valve main body 19 bends towards the first fuel outlet 25, allowing fuel in the fuel pressurization chamber 32 to flow through the first fuel outlet 25 and the high-pressure fuel discharge passage 7 into the high-pressure damper 8, where fuel pressure surges are absorbed. Fuel pressure surges in the high-pressure fuel are additionally absorbed by the orifice 11 which is disposed downstream from the high-pressure damper 8. After surges have been removed, the high-pressure fuel is supplied to a delivery pipe 13 via a fuel discharge port 15 and a high-pressure pipe 16 formed in an end portion of the high-pressure fuel discharge passage 7, and thereafter supplied to each of the cylinders (not shown) of the engine via the fuel injection valves 14.
In a high-pressure fuel supply assembly 100 of the above construction, the high-pressure damper 8 and the orifice 11 are provided to stabilize the amount of fuel injected by the fuel injection valves 14 and to prevent amplification of surges due to resonation of the delivery pipe 13 which results from fuel pressure surges in the high-pressure fuel discharged from the high-pressure fuel pump 6.
FIG. 9 shows data obtained experimentally by the present inventors for the average pressure in the high-pressure fuel supply assembly 100 for orifices 11 of different sizes. It can be seen that the pressure in the high-pressure fuel supply assembly 100 is higher than when there is no orifice 11 and that the pressure in the high-pressure fuel supply assembly 100 increases as the diameter of the bore in the orifice 11 is reduced.
Furthermore, FIG. 10 shows the surge pressure (the difference between high and low pressure) in the delivery pipe 13. It can be seen that the surge pressure in the delivery pipe 13 is smaller than when there is no orifice 11 and that the surge pressure in the delivery pipe 13 is further reduced as the diameter of the bore the orifice 11 is reduced.
In a high-pressure fuel supply assembly 100 of the above construction, the orifice 11 is disposed upstream from the high-pressure regulator 10 and as shown in FIG. 9, when the flow discharged from the high-pressure fuel pump 6 is increased in the high rotational frequency region of the engine, the loss of pressure in the orifice 11 increases, and since the high-pressure regulator 10 adjusts the pressure in the delivery pipe to a predetermined level, the fluid pressure from the fuel pressurization chamber 32 to just upstream of the orifice 11 is raised proportionately to this loss in pressure. For that reason, one problem has been that excessive loads are placed on the high-pressure fuel pump 6, the high-pressure damper 8, and the cam shaft which drives the high-pressure fuel pump 6, reducing the working life of the high-pressure damper 8 and the cam shaft.
Another problem has been that the range of the working pressure of the high-pressure damper 8 has had to be enlarged.
Furthermore, when the diameter of the orifice 11 is reduced in order to reduce surge pressure in the delivery pipe 13 further, the loss of pressure at the orifice 11 increases proportionately, raising the fuel pressure in the fuel pressurization chamber 32, and another problem has been that when the fuel pressure rises too high, the flow discharged from the high-pressure fuel pump 6 is reduced. This problem has been particularly evident in the high rotational frequency region where the flow discharged from the high-pressure fuel pump 6 is increased.